The uses of energy in the United States during the past century have been developed during a period of cheap energy. As a result many uses have been designed that are quite wasteful from an energy point of view, but economic in the overall point of view. With sharply rising costs of energy in recent times, many designs for energy that were economically attractive in the past are becoming economically unsound in the face of rising energy costs. As a result buildings that were not insulated in the past because it was cheaper to waste fuel than to pay for insulation are now being insulated, designs for processes that were basically wasteful of energy are undergoing redesign, and the like.
It is well known in the art how to generate steam by burning a source of energy and then expanding the steam through a turbine to generate electricity. This process is basically wasteful of energy because in heating water it requires one BTU of heat to raise one pound one degree Farenheit; at the point water is converted from liquid to vapor, approximately 1000 BTUs of heat are required for each pound of water vaporized; upon becoming dry vapor the steam may be raised to higher temperatures with modest increases in heat added per pound of steam; the steam is expanded through a turbine which in turn generates electricity; then the remaining steam is condensed to water by giving up approximately 1000 BTUs per pound to the cooling towers and cooling ponds. It is this latter heat loss that significantly diminishes the overall efficiency of the process where efficiencies in the order of 33% are common.
The electric generating industry has devoted considerable research in an attempt to minimize these losses without notable success. One scheme has been to pull a partial vacuum on the discharge side of the turbine to lower the boiling point of water to temperatures in the atmospheric air range. Another scheme is to eleminate the low pressure turbine and deliver steam from the intermediate pressure turbine to a metropolitan area where the steam is used for the heating of buildings with the condensate returned to the steam-electric generating station for recycling. In the first scheme enormous quantities of low grade heat are wasted by heating the water of cooling ponds or lakes so that approximately one pound of water will be evaporated for each pound of steam condensed. In the second scheme the use of steam for heating buildings must of necessity be limited to the requirements of the buildings for heat.
In general an electric generating station must be operated at different rates of output to meet the demand for electricity. This demand may vary widely over a 24 hour period, which adds complications to plans for utilization of heat that otherwise would be wasted.
One industry that uses a considerable amount of heat each 24 hours on a year around basis is sulphur mining using the Frasch process. In this process water is heated to a temperature well above the melting point of sulfur (240.degree. F) and is kept under pressure as water to avoid the heat requirement necessary to convert water to vapor and the heat loss of converting the vapor back to water. At the sulphur mine the water is brought up to temperature in the typical range of 330.degree. to 360.degree. F for injection into the underground sulphur formation. A typical sulphur mine will have a multiplicity of sulphur wells, each well having a capability of taking water over a wide range of injection rates. It is this flexibility in taking water in the individual wells that makes a Frasch process sulphur mine an ideal candidate to couple with a steam-electric generating station because the swing in electric output requirements can be matched with a corresponding swing in the hot water input to the sulphur mine. These swings can be accomplished without regard to the time of day or to the season of the year.